Tunable coaxial cavity resonator



Aug. 15, 1967 K. E. HANCOCK 3,336,542

TUNABLE COAXIAL CAVITY RESONATOR Filed Sept. 5, 1965 2 Sheets-Sheet 1LV/,/////////////////A INVENTOR K. E. HANCOCK ATTORNEYS Aug. 15, 1967 K.E. HANCOCK 3,336,542

TUNABLE. COAXIAL CAVITY RESONATOR Filed Sept. 3, 1965 2 Sheets-Sheet 2CYLINDR ICAL CQP MODIFIED CUP RETRACTION FREQUENCY 9 FIG. 2

INVENTOR K. E. HANCOCK A TTORNEYS United States Patent 3,336,542 TUNABLECUAXIAL CAVITY RESONATOR Kenneth E. Hancock, Roxboro, Quebec, Canada,assignor to Canadian Marconi Company, Montreal, Quebec, Canada FiledSept. 3, 1965, Ser. No. 484,973 1 Claim. (Cl. 33382) This invention isconcerned with tunable cavity resonators and is particularly directed tocavities of the coaxial type having capacity loading.

A reduction in the length of coaxial cavities which are tuned over arange of frequencies by adjustment of the length of the inner conductorcan be achieved by fixing a capacity loading cup coaxially on that endwall opposite the wall supporting the inner conductor. The loading cup,cylindrical in configuration, has an inner diameter somewhat larger thanthe free end of the coaxial inner conductor. In tuning the device theinner conductor penetrates beyond the lips of the cup member, and inadvancing increasingly loads the inner conductor with end capacity.

The above-described arrangement has the disadvantage in someapplications that the change of frequency obtained is a quite non-linearfunction of the axial displacement of the inner conductor. It is an aimof this invention to substantially reduce this non-linearity.

According to the invention a tunable coaxial resonator of the typewherein the free end of the coaxial inner conductor is adjustableaxially to enter within the confines of a cylindrical cup-shapedcapacity loading member is characterised in that the wall of saidcup-shaped member is provided with a pair of diametrically oppositesemi-circular cut-outs the radius of which is subsantially the same asthe inner radius of said cup-shaped member and whose centres lie in theplane of the cup rim.

The invention will be more particularly described with reference to theaccompanying drawings in which:

FIGURE 1 shows in cross-section a tunable coaxial cavity resonator inaccordance with the invention; and

FIGURE 2 shows the tuning laws of a resonator in ac cordance with theinvention as compared with that of a prior art cavity.

Referring to FIGURE 1 there is shown a tunable coaxial cavity resonatorcomprising the known construction of a cylinder 1, end walls 2 and 3, afixed section of coaxial inner conductor 4, an axially moveable innerconductor section 5 with actuating means such as screw 6, and a capacityloading cup 7. In accordance with the invention the cup 7 is providedwith two diametrically opposite semi-circular cut-outs, one of which, 8,is visible in FIGURE 1. As is shown, the cut-outs have a radius which issubstantially the same as that of the inner radius of cup 7, and areoriented such that their centres lie on a common diameter in the planeof the cup rim.

In FIGURE 2 is shown the tuning law for such a cavity with and withoutthe cut-outs 8. It will be seen that by the use of cut-outs 8 inaccordance with the invention a substantial improvement in the linearityof the tuning law is achieved.

I claim:

A tunable coaxial resonator of the type wherein the free end of thecoaxial inner conductor is adjustable axially to enter within theconfines of a cylindrical cupshaped capacity loading member ischaracterised in that the wall of said cup-shaped member is providedwith a pair of diametrically opposite semi-circular cut-outs the radiusof which is substantially the same as the inner radius of saidcup-shaped member and whose centres lie in the plane of the cup rim.

No references cited.

ELI LIEBERMAN, Primary Examiner. L. ALLAHUT, Assistant Examiner.

